Speed/rpm sensors use different operating principles – Hall-effect, magnetoresistive, inductive – to detect, without contact, rotary motion of phonic wheels or gears and in general of any rotating iron object with slits or protruding parts.
A digital frequency output signal – in the Hall-effect or magnetoresistive versions – or an alternate wave – in the inductive versions – correspond exactly to the full or the vacuum of the rotating object.
ISpeed and direction sensors have two digital frequency outputs. By reading signals A and B the clockwise or anti-clockwise direction of the wheel can be determined. The phase difference between the two signals determines the direction of the rotation.
Performances differ, depending on which technology is used: gap (sensor-wheel distance); connection (2/3 poles); costs.
They find typical application on engines, differentials, transmissions, turbines, pumps, gear racks and can operate under the most severe conditions.